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| SOL | MERCURY | VENUS | EARTH | METEORS | MOON | MARS | ASTEROIDS | JUPITER | SATURN | URANUS | NEPTUNE | PLUTO | COMETS |
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| SOL | MERCURY | VENUS | EARTH | METEORS | MOON | MARS | ASTEROIDS | JUPITER | SATURN | URANUS | NEPTUNE | PLUTO | COMETS |
The Solar System. Our Solar System. Our little corner of the Universe. Our little oasis of light, and heat, and matter, in the limitless dark, and cold, and emptiness of space. Beyond our Solar System there is nothing, for a very long way. The nearest star, Proxima Centauri, is over four light years distant, and it may as well be four million. We may never develop the technology to travel that far. So for a very long time, and possibly forever, this Solar system is all we have. It is not just our neighborhood, it is the only neighborhood we will most likely ever know, and that makes it somewhat important.
It all started more than five billion years ago. In one of the arms of a great spiral galaxy that came to be known as the Milky Way, about two thirds of the way out from the center, a few scattered atoms and molecules began to congregate. Gases formed. Microscopic bits of intersteller dust wandered into the mix. Forces of mutual attraction - the beginnings of gravity - began to work, drawing more and more material together.
It took a very long time, but eventually a huge cloud of gas and dust formed. When it got to be many billions of miles across, it began to take on a life of its own, heating up, and rotating. An intense gravity well formed at the center that pulled everything inwards. The more material pulled into the center of the cloud, the denser it became, and the more gravity and heat was produced, until finally the density and the heat became extreme enough to finally ignite, and a star - our Sun - was born. Below are actual photos of a protoplanetary disk around a newly formed star in the Great Orion Nebula, captured by NASA's Hubble Space Telescope.
99.8 % of the cloud was either consumed in the birth of the Sun, or drawn in by its immense gravity shortly thereafter. The 0.2% that was left over gradually flattened into a protoplanetary disk, and eventually became everything else in the solar system, including all the planets and their moons, and all the thousands of asteroids and comets, and everything else in the Solar System, including you and me.
The photo composite above shows all eight planets in their proper order from the Sun, and accurately shows their sizes, relative to each other and to the Sun. You can easily see how the huge mass of the Sun contains 99.8 % of all the matter in our solar system, and how small and frail our tiny little blue/white home is. But although the above picture is scientifically to scale as far as size goes, distance is another matter entirely. The fact is the planets in our solar system are extremely far apart, and our solar system is really quite an empty place.
If the Sun was only one inch (2.54cm) in diameter, Earth would be the size of a small grain of sand almost 10 feet (3 meters) away. Giant Jupiter would be a large grain of sand almost 50 feet (16 meters) away. Uranus would be a medium sized grain of sand 170 feet (57 meters) away! And believe it or not, poor little I-was-once-a-planet Pluto would be only the size of grain of salt way out at 350 feet (118 meters) away from our little one inch Sun! That our technology can detect such a small object so far away is a bit of a miracle all by itself.
The diagram below accurately shows the relative distances of all the planets from the Sun, and from each other. For size to be to scale as well, you would have to reduce the Sun to a speck of dust, and all the planets to microscopic pin-pricks. The solar system is a very big place, and like the Universe itself (as far as we can detect), mostly cold, empty space.
You can see how the four small solid planets of the inner solar system are all clustered tightly around the Sun, while beyond the asteroid belt, the four giant gas planets of the outer solar system are spread very far apart, a very long way from the warmth and light of the Sun.
Below is an Orrery, a real time graphical representation of the relative positions of the planets in our Solar System. It keeps track of exactly where each planet is, as it moves in its orbit around the Sun, and shows us where all the planets are right now. An Orrery is a great tool for gaining a more enlightened perception of how our solar system works. You can readily see why, when viewed from Earth, the other planets sometimes appear close together, when they're not really close together at all. Or why they appear close to the Sun, in the morning or evening sky.
Beyond the planets lies the Kuiper Belt, a region full of chunks of icy debris, some of which are large enough to be classified as dwarf planets, including the former planet Pluto.
Beyond the Kuiper Belt, the gravity of the Sun is not strong enough to keep the chunks of ice and rock that reside there in the same plane as the planets, so that they spread out into a sparsely populated sphere of debris, referred to as the Oort Cloud. When a piece of this debris is disturbed by changing gravitational forces inside or outside our Solar System, and it begins to fall toward the Sun, a comet is born.
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